Toward probabilistic post-fire debris-flow hazard decision support

Bulletin of the American Meteorological Society
By: , and 



Post-wildfire debris flows (PFDF) threaten life and property in western North America. They are triggered by short-duration, high-intensity rainfall. Following a wildfire, rainfall thresholds are developed that, if exceeded, indicate high likelihood of a PFDF. Existing weather forecast products allow forecasters to identify favorable atmospheric conditions for rainfall intensities that may exceed established thresholds at lead times needed for decision-making (e.g., ≥24 h). However, at these lead times, considerable uncertainty exists regarding rainfall intensity and whether the high-intensity rainfall will intersect the burn area. The approach of messaging on potential hazards given favorable conditions is generally effective in avoiding unanticipated PFDF impacts, but may lead to “messaging fatigue” if favorable triggering conditions are forecast numerous times, yet no PFDF occurs (i.e., false alarm). Forecasters and emergency managers need additional tools that increase their confidence regarding occurrence of short-duration, high-intensity rainfall as well as tools that tie rainfall forecasts to potential PFDF outcomes. We present a concept for probabilistic tools that evaluate PFDF hazards by coupling a high-resolution (1-km), large (100-member) ensemble 24-h precipitation forecast at 5-min resolution with PFDF likelihood and volume models. The observed 15-min maximum rainfall intensities are captured within the ensemble spread, though in highest ∼10% of members. We visualize the model output in several ways to demonstrate most likely and most extreme outcomes and to characterize uncertainty. Our experiment highlights the benefits and limitations of this approach, and provides an initial step toward further developing situational awareness and impact-based decision-support tools for forecasting PFDF hazards.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Toward probabilistic post-fire debris-flow hazard decision support
Series title Bulletin of the American Meteorological Society
DOI 10.1175/BAMS-D-22-0188.1
Volume 104
Issue 9
Year Published 2023
Language English
Publisher American Meteorological Society
Contributing office(s) Geologic Hazards Science Center - Seismology / Geomagnetism
Description 19 p.
First page E1587
Last page E1605
Country United States
State California
City Montecito
Other Geospatial Santa Ynez Mountains
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